Ortho-functionalized perylenediimides for highly fluorescent water-soluble dyes

Clearly visible: A water-soluble and highly fluorescent perylenediimide is synthesized via ruthenium-catalyzed alkylation with outstanding yields. For the first time, the possibility to use phosphonate derivatives in a Murai-type reaction is demonstrated.     

Towards highly fluorescent and water-soluble perylene dyes

A systematic approach towards highly fluorescent, water-soluble perylene-3,4:9,10-tetracarboxylic acid diimide chromophores is presented. Water solubility was introduced first through the attachment of four hydrophilic substituents onto the bay region of the perylene dye. Positively and negatively charged groups were then applied to the chromophore, and their number and their distance from the aromatic scaffold were systematically varied. To suppress aggregation, the chromophore was further isolated within a dendritic shell. Such variation of structural features and a thorough investigation of the resulting optical properties facilitated the first synthesis of perylene-3,4:9,10-tetracarboxylic acid diimides combining the properties of water solubility and fluorescence quantum yields (FQYs) close to unity, which makes them attractive as high-performance fluorescence probes in aqueous media.     

In situ preparation of a highly active N-heterocyclic carbene-coordinated olefin metathesis catalyst

Highly active N-heterocyclic carbene-coordinated catalysts may be synthesized and used in situ, without requiring prior isolation of the catalyst. Activation of this in situ catalyst with ethereal HCl dramatically reduces the reaction times required for high conversions. A variety of alpha,beta-unsaturated carbonyl-containing substrates participate readily in cross and ring-closing metathesis reactions using this preparation.     

Squaraine-derived rotaxanes: highly stable, fluorescent near-IR dyes

Squaraines are fluorescent, near-IR dyes with promising photophysical properties for biomedical applications. A limitation with these dyes is their inherent reactivity with nucleophiles, which leads to loss of the chromophore. Another drawback is their tendency to form nonfluorescent aggregates in water. Both problems can be greatly attenuated by encapsulating the dye inside an amide-containing macrocycle. In other words, the squaraine becomes the thread component in a Leigh-type rotaxane, a permanently interlocked molecule. Two new rotaxanes are described: an analogue with four tri(ethyleneoxy) chains on the squaraine to enhance water solubility, and a rotaxane that has an encapsulating macrocycle with transposed carbonyl groups. An X-ray crystal structure of the latter rotaxane shows that the macrocycle provides only partial protection of the electrophilic cyclobutene core of the squaraine thread. The stabilities of each compound in various solvents, including serum, were compared with a commercially available cyanine dye. The squaraine rotaxane architecture is remarkably resistant to chemical and photochemical degradation, and likely to be very useful as a versatile fluorescent scaffold for constructing various types of highly stable, near-IR imaging probes.     

Dipolar 3-methoxychromones as bright and highly solvatochromic fluorescent dyes

Herein, three environment-sensitive (solvatochromic) fluorescent dyes presenting a strong electron acceptor 3-methoxychromone unit and varied electron donor 2-aryl were developed. All three dyes showed remarkable polarity-dependent shifts of the emission maximum, which increase with extension of the dye conjugation. For the 3-methoxychromone bearing a 7-(diethylamino)-9,9-dimethylfluoren-2-yl donor group the difference between the excited and the ground state dipole moments, estimated from the Lippert-Mataga expression, reached 20 D, which is among the largest reported for neutral dipolar fluorophores. Moreover, the new dyes are characterized by significant two-photon absorption cross-section (up to 450 GM) and large fluorescence quantum yields. The strong decrease in the fluorescence quantum yields of the dyes in polar protic solvents was observed together with the increase in the non-radiative deactivation rates, which can originate from twisted intramolecular charge transfer and intermolecular proton transfer phenomena. In comparison to the parent 3-hydroxychromone derivatives, the new dyes presented significantly improved photostability, which confirms that photodegradation of 3-hydroxychromones occurs from a product of the excited-state intramolecular proton transfer (phototautomer). Finally, an application of the new dyes for probing local binding site polarity of serum albumin was shown. This new class of fluorescent dyes may serve as attractive building blocks for future molecular sensors utilizing environment-sensitive fluorophores.     

Conformationally restricted aza-BODIPY: highly fluorescent, stable near-infrared absorbing dyes

Novel NIR fluorescent, conformational restricted aza-dipyrromethene boron difluoride (aza-BODIPY) dyes were prepared by an efficient process. Such conformational restricted aza-BODIPY dyes possess intense absorption, strong fluorescence, high chemical and photostability. Additionally, the sharp fluorescence of non-amine containing aza-BODIPY dyes is insensitive to solvent polarity.     

Large geometrical structure changes of photochromic diarylethenes upon photoirradiation

Photochromic diarylethene derivatives having phenylethynyl and pent-1-ynyl groups at the reactive carbons have been synthesized. These ethynyl groups enhance the cycloreversion quantum yields of diarylethenes without affecting the absorption maxima and the absorption coefficients of the closed-ring isomers. The derivatives exhibited large geometrical structural changes in the photoisomerization process.     

Large Stokes shift fluorescent dyes based on a highly substituted terephthalic acid core

The synthesis of dyes based on a highly substituted terephthalic acid core is described, starting from readily available 2,5-dihydroxy-terephthalic acid diethyl ester. The dyes are highly colored, soluble in organic solvents and reasonably fluorescent in solution and in the solid state. The maxima for absorption and emission are around 402 and 502 nm, respectively. The fluorophores are readily cyclized to generate compounds which comprise the basic 6,13-dihydroxy-chromeno[2,3-b]xanthene-7,14-dione unit. These new derivatives are nonfluorescent.     

In situ generation of highly active olefin metathesis initiators

A ruthenium based benzylidene complex bearing an O,N-bidentate Schiff base ligand exhibits poor olefin metathesis activity but generates a highly active catalyst system when treated with acidic cocatalysts. Various Lewis acids were able to boost the ring opening metathesis polymerization (ROMP) of cycloocta-1,5-diene (COD). The best results were obtained with trichlorosilane (HSiCl₃), which was also found to improve metathesis activity of the Grubbs second generation catalyst [RuCl₂(CHPh)(H₂IMes)(PCy₃)] in the ROMP of COD and the ring closing metathesis (RCM) of diethyl diallylmalonate.     

Axially chiral bichromophoric fluorescent dyes

A new life for Kurt Mislow's authentic amines: Diaminobiphenyls were applied as the framework materials for the synthesis of axially chiral bichromophoric systems with strong CD and CPL effects.     

In situ preparation and surface modification of magnesium hydroxide nanoparticles

Hydrophobic magnesium hydroxide (Mg(OH)₂) nanoparticles were successfully synthesized via a one-step solution precipitation method with octadecyl dihydrogen phosphate (n-C₁₈H₃₇OPO₃H₂, ODP) as a surface modifier. The ODP was used to control the growth of crystal in the c direction (direction perpendicular to the layers) and to modify the surface property of the Mg(OH)₂ particles produced from the precipitation. Measurements of relative contact angle and active ratio indicated that Mg(OH)₂ samples were hydrophobic. The samples were characterized by using field emission scanning electron microscope (SEM), X-ray diffraction (XRD), infrared analysis (IR). The mechanism of influence of ODP on the surface property and morphology of Mg(OH)₂ was discussed. Furthermore, from the results of the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) tests, it was confirmed that small amount of magnesium alkyl phosphate on the surface of Mg(OH)₂ particles enhanced the thermal stability of the low density polyethylene(LDPE)/Mg(OH)₂.     

Spectroscopic studies of fluorescent perylene dyes

The lowest electronic transition of the fluorescent perylene dye bis-(3,5-di-tertbutylphenyl)-perylene-3, 4:9,10-biscarboximide has been investigated b     

Site-selective monotitanation of dialkynylpyridines and its application for preparation of highly fluorescent pi-conjugated oligomers

Reaction of Ti(O-i-Pr)(4)/2i-PrMgCl reagent with 2,n-bis[(trimethylsilyl)ethynyl]pyridines, where n is 3, 4, 5, and 6, or with 3,4-bis[(trimethylsilyl)ethynyl]pyridines, proceeded with excellent site-selectivity to afford the corresponding monotitanated complex. Synthetic application of the reaction was demonstrated by an efficient preparation of pi-conjugated oligomers having pyridine and enyne units alternately, which possess intense blue fluorescence emission.     

Easy preparation and characterization of highly fluorescent polymer composite microspheres from aqueous CdTe nanocrystals

Fluorescent microspheres were easily fabricated from aqueous CdTe nanocrystals (NCs). The NCs, which had negative charges on the surface, were first extracted to chloroform by cationic surfactant octadecyl-p-vinyl-benzyldimethylammonium chloride (OVDAC) and then swollen into performed polystyrene (PS) microspheres. Through this method, strong photoluminescence (PL) of aqueous NCs was inherited in the resultant composite microspheres. Moreover, the NCs were firmly stabilized in the microspheres, withstanding not only polar solvents but also nonpolar solvents. UV-vis spectrum, PL spectrum, TEM, and confocal fluorescence microscopy were used to characterize the product.     

In situ preparation of oxide-based supported catalysts by solution combustion synthesis

The oxide-based supported catalysts with high specific surface area (>200 m(2)/g) were produced in one step through combination of the impregnation and solution combustion synthesis approaches. As a model system, iron oxide was selected, which was loaded on different porous supports including alpha-Al(2)O(3), gamma-Al(2)O(3), and ZrO(2), as well as activated alumina. It was shown that for the former three cases the specific surface areas of the supported catalysts are about or below the surface areas of the support. However, for the activated Al(2)O(3) this characteristic significantly increases compared to that of the support. It was demonstrated that the developed approach may be used to produce different types of oxide-based supported catalysts, including perovskites.     

Cell-permeable iminocoumarine-based fluorescent dyes for mitochondria

A class of small molecule fluorophores, 2-iminocoumarin-3-carboxamide derivatives, has been developed by a rapid microwave-assisted process. These fluorescent probes are cell membrane permeable with low cytotoxicity and able to selectively stain organelles in living cells.     

Rotational barriers in perylene fluorescent dyes

Rotational barriers in N-substituted perylene dyes have been determined. Phenyl substituents with tert-butyl groups in the o-position give rigid systems, whereas secondary alkyl groups cause low rotational barriers. In spite of that, fluorescent quantum yields are high in both cases. Conformations in solution are discussed.     

In situ preparation of Al-containing PVDF ultrafiltration membrane via sol-gel process

Recently, inorganic nanoparticles blended within polymeric membranes have shown improved antifouling performance in wastewater treatment. However, agglomeration of nanoparticles remains as one of the major obstacles for generating a uniform surface. In this study, a new method for in situ preparation of Al-containing PVDF ultrafiltration membranes to improve the dispersion of nanoparticles is reported. The strategy of this method is to combine sol-gel process with traditional immersion precipitation process. Al sol was synthesized by the addition of anionic exchange resin in N,N-dimethylformamide (DMF) solvent containing aluminum chloride. Homogeneous Al-containing PVDF casting solution was then obtained by dissolving PVDF polymer in the Al sol. The membrane formation mechanism was investigated by precipitation kinetics and morphology. Results indicate that the addition of Al species can accelerate phase inversion of casting solution. Scanning electron microscopic images show that a typical transition from sponge-like structure to finger-like structure occurred with increasing Al species content. The existence and dispersion states of Al species in the resultant membrane matrix were further examined by transmission electron microscope and X-ray photoelectron spectrometer. The results indicate the Al species nanoparticles were well dispersed throughout PVDF matrix. Dynamic BSA fouling resistance experiments demonstrate the Al-containing PVDF membranes possess improved separation performances over the pure PVDF membranes.